1. Field of the Invention
This invention relates to novel isocyanate containing compositions and to a process for their preparation and is more particularly concerned with novel, storage stable prepolymer compositions derived from polymethylene polyphenylisocyanates.
2. Description of the Prior Art
The formation of storage stable liquid isocyanate containing compositions derived from pure methylenebis(phenylisocyanate) and minor amounts of a diol are known in the art; see U.S. Pat. Nos. 3,394,164 and 3,394,165. Storage stable liquid isocyanate compositions having an average isocyanate functionality greater than 2 and which do not crystallize, have been prepared from polymethylene poly(phenylisocyanates) and a polyoxyalkylene diol or alkylene diol as disclosed in German Pat. application No. 2,513,793. Liquid mixtures consisting of polymethylene poly(phenylisocyanates) and methylenebis(phenylisocyanate) partly reacted with a glycol have been disclosed in German Patent Application No. 2,513,796.
The polymethylene polyphenylisocyanates referred to hereinabove are generally produced by phosgenation of a mixture of polyamines produced by acid condensation of formaldehyde and aniline; see for example, U.S. Pat. Nos. 2,683,730, 2,950,263, and 3,012,008.
Storage stable liquid isocyanate prepolymer compositions are useful in the preparation of molded polyurethane parts, and microcellular shoe soles; see "Microcellular Elastomers in Footwear," by P. S. Carleton, J. H. Ewen, H. E. Reymore, and A. A. R. Sayigh, J. Cellular Plastics, Vol. 10, page 1, 1974. A particularly advantageous method for the preparation of polyurethanes in which storage stable liquid isocyanate prepolymers find particular utility is referred to synonymously as liquid reaction molding (LRM) or reaction injection molding (RIM); see Liquid Reaction Molded Polyurethanes by F. E. Critchfield, National Technical Conference of the Society of Plastics Engineers, page 64, Nov. 12, 1974 for a detailed discussion of the method.
For an isocyanate composition to be useful in RIM technology, it must meet certain requirements with respect to such factors as isocyanate functionality, viscosity, storage stability, polymer demolding characteristics, and particularly the mechanical properties of the polyurethane material produced therefrom.
We have unexpectedly discovered that when a polyoxyethylene glycol which falls within a specifically narrow molecular weight range is reacted with a polymethylene polyphenylisocyanate within a narrow range of proportions there are produced storage stable liquid isocyanate prepolymer compositions which possess the requisite properties to allow their use in RIM technology and microcellular shoe sole preparation. Surprisingly, the isocyanate compositions give rise to polyurethane polymers which have superior mechanical and demolding properties compared to those polyurethanes prepared from the storage stable isocyanates prepared in accordance with the prior art.